As a result, the shape of a yield curve (where the Y-axis shows rising interest rates and the X-axis shows increasing time durations) is a line beginning on the lower left side and rising to the upper right side. This curved line is referred to as a “normal” yield curve.

The Factors That Influence the Yield Curve

Keeping in mind that bond prices and yields move in opposite directions, different factors influence movements on either end of the yield curve. Short-term interest rates—also called "the short end" of the yield curve—tend to be influenced by what the government is going to do in the future, or specifically, expectations for U.S. Federal Reserve policy. These short-term rates tend to rise when the Fed is expected to raise interest rates and fall when it's expected to cut rates.

Long-term bonds—"the long end” of the curve—are also influenced to some extent by the outlook for Fed policy, but other factors play a role in moving long-term yields either up or down.

Foremost among these factors are the outlook for inflation, economic growth, supply-and-demand and investors’ general attitude toward risk.

All these factors push and pull simultaneously to influence the direction of long-term bonds.

Shapes of the Yield Curve

The yield curve is always changing based on shifts in general market conditions. It can steepen because long-term rates are rising faster than short-term rates (thus indicating underperformance for long-term bonds versus short-term issues). Conversely, the yield curve can flatten, which means that short-term rates are rising faster than long-term rates (thus indicating outperformance for long-term bonds relative to short-term issues).

Very rarely, the yield curve can be inverted. This occurs when short-term bonds are actually yielding more than long-term issues, or when the curve trends down and to the right rather than upward. An inverted yield curve usually occurs when investors expect an environment of sharply slowing economic growth, low inflation, and future interest rate cuts by the Federal Reserve.